1. Field of the Invention
The present invention relates to a multi-cylinder internal combustion engine, in which at least some of a plurality of cylinders are capable of selectively resting during engine operation under low load.
2. Description of the Background Art
Among multiple-cylinder internal combustion engines, an engine is known in which some of the cylinders selectively rest, or become non-operative, during normal engine operation under certain low-load conditions. With some of the cylinders being permitted to rest during normal engine operation, it is possible to obtain an improvement in fuel consumption at the time of a low-load operation or the like, and also to produce extra power when needed, by operating all the cylinders at the time of a high-load operation. Specifically, there is a known system in which an engine control is performed that permits an increase the number of operating cylinders from two cylinders to three cylinders and, further, to four cylinders attendant on the transition from a low-load operation to a high-load operation. Such an engine is disclosed, for example, in Japanese Laid-open Patent publication No. Hei 08-105337.
In Japanese Laid-open Patent publication No. Hei 08-105337, an ignition-retarding operation is carried out, for suppressing a forward surge, arising from an increase in engine torque, which would otherwise be experienced at the time of changeover at a time when a cylinder transitions from a resting mode to an operating mode. It has become apparent, however, that control of the intake air quantity is effective for obtaining a further suppression of output variation during transitional periods. However, in the case of controlling the intake air quantity by using a single throttle valve, a high response performance is required for driving the throttle valve, at the time of changing over the number of cylinders. As a result, manufacturing costs are increased in order to realize the high performance response. In addition, in order to control the intake quantities for a plurality of cylinders by use of a single throttle valve, a complicated control system is needed.
In view of the foregoing, it is an object of the present invention to provide an internal combustion engine which is capable of selectively resting some of the engine cylinders, which does not need a high performance response in operating throttle valves, and which can eliminate a step change in engine output at the time of changing the number of operating cylinders.